That's all it does? No change to abilities or helping to unlock trophies?

I don't know what trophies you're talking about, but yes, that's all it does. If you want to change abilities you use the enchant tab or reroll it using the cube.

Would be hella OP if it just gave you the item.

Always weirds me out when people ask stuff like this on the forums instead of just googling it.

What a weird question. Transmogrification has been a concept since 2011. And, yeah, a quick Google search would have yielded much faster and better results...

That's literally what the word means...

No, that's Arqade. This is a place where people can have meaningful (or occasionally non-meaningful) discourse on video games (or occasionally non-video games).